1. Field of the Invention
The present invention relates to water-bearing explosive compositions of the water-in-oil emulsion type which contain an aqueous solution of inorganic oxidizing salt as a dispersed phase within a continuous carbonaceous fuel phase, and to an improved method of preparing such compositions.
2. Description of the Prior Art
Water-bearing explosives of the emulsion type have become increasingly attractive in recent years because they can provide the advantages of gelled or thickened water-bearing explosives in terms of performance and safety while being simpler to manufacture and lower in ingredients cost than the gelled products, which require a gelling agent to inhibit component separation and to improve water resistance.
In U.S. Pat. No. 3,447,978, Bluhm describes water-in-oil emulsion blasting agents in which the carbonaceous fuel contains wax and has a consistency such as to hold a specified volume of occluded gas in the emulsion at a temperature of 21.degree. C. Emulsifying agents specifically disclosed generally are of the nonionic type, e.g., sorbitan fatty acid esters. These blasting agents are reported to be capable of being detonated, after storage for 28 days at 21.degree. C., by an 8 cm.times.8 cm dynamite cartridge. U.S. Pat. Nos. 3,715,247 3,765,964, 4,110,134, 4,138,281, and 4,149,917 describe Bluhm's blasting emulsions modified in various ways to render them cap-sensitive.
Compositions in which ammonium nitrate-containing emulsions are combined with solid ammonium nitrate, ANFO, and gelled explosives are described in U.S. Pat. Nos. 3,161,551, 4,111,727, and 4,104,092, respectively.
In addition to the nonionic emulsifiers described in the Bluhm and related patents, salts of fatty acids also have been used in emulsion-type explosives. For example, in U.S. Pat. No. 3,770,522, Tomic describes the use of a stearate salt, preferably in combination with stearic acid to shorten the emulsification time. This emulsifying system also is described in U.S. Pat. No. 4,008,108. Chrisp, in U.S. Pat. No. 3,706,607, additionally mentions sodium oleate with or without oleic acid, while Cattermole et al., in U.S. Pat. No. 3,674,578, specify calcium, magnesium, and aluminum oleates.
Improvements are needed in the storage stability, or shelf life, of water-in-oil emulsion explosives of the type described above. It goes without saying that however acceptable the explosive properties of the composition may be at the time of manufacture, the composition must retain its ability to perform in the required manner after exposure to the conditions prevailing in storage areas, in transportation vehicles, and in the field. While the explosive properties, e.g., detonation velocity, brisance, and ease of initiation, of an emulsion explosive are related in large measure to the specific oxidizer/fuel system and sensitizing materials therein, these properties also are greatly affected by the physical structure of the composition. Reliability of performance as an explosive requires that the necessary dispersion of the oxidizer salt-containing aqueous phase, in a suitable cell size, in the continuous carbonaceous fuel phase be maintained. While there has been some reference in the art to the storage stability, or shelf life, of certain emulsion-type explosives, the disclosures have been limited to storage at only about 21.degree. C. or lower. Also, some of the compositions which employ the economically attractive anionic emulsifying agents require undesirably heavy primers or boosters to effect their detonation after storage.
It is not unlikely that an emulsion blasting agent will be exposed to temperatures above 21.degree. C. for various periods of time during storage, while being transported, or after being deposited at the place of use. Therefore, the art of blasting is in need of emulsion explosives whose chemical composition and/or physical structure is not deleteriously changed, i.e., whose explosive properties are preserved, after exposure to temperatures above 21.degree. C., e.g., up to at least 32.degree. C. and perhaps as high as at least about 49.degree. C. With specific regard to explosive emulsions employing anionic emulsifying agents, emulsions of this type which can be detonated by a relatively small primer after storage even at temperatures no higher than about 21.degree. C. also would be useful to the art, although such compositions which also are stable at higher temperatures would doubtlessly achieve wider acceptance.